(i) Field of the Invention
The present invention relates to a carbon fiber-reinforced cement material containing carbon fiber as a reinforcing material and having a high reinforcing effect, and it also relates to a method for preparing the above-mentioned carbon fiber-reinforced cement material.
(ii) Description of the Prior Art
Cement materials such as mortar and concrete are inexpensive and excellent in durability, fire resistance and other physical properties such as compression strength and stiffness. Thus, they have been widely used as construction materials and building materials. In these cement materials, tensile strength and impact resistance are low in contrast to the compression strength, and an energy absorption ability is poor. Accordingly, the cement materials have the drawback that they are "brittle" from the viewpoint of physical properties. In addition, the cement materials do not have any conductivity, and so when they are used as floor materials, a special treatment such as an antistatic treatment is required on occasion. For the purpose of solving these problems, fiber-reinforced cement materials reinforced with various fibers have been often used. Above all, much attention is paid to fiber-reinforced cement materials containing a carbon fiber as a reinforcing material which are characterized by having good chemical stability typified by alkali resistance, good heat resistance, large strength and elasticity, high conductivity and light specific gravity.
However, in the cement material reinforced with a short carbon fiber, the tensile strength and bending strength of the cement material are not sufficiently improved in proportion to the tensile strength which the carbon fiber inherently has, and there is the problem that values of the strength widely scatter in a series of products or even in one product. The cause of these drawbacks can be considered to be as follows: In the short carbon fiber-reinforced cement material, the adhesion of a cement matrix to the carbon fiber is not sufficient, so that the reinforcing ability of the carbon fiber is not exerted. In consequence, the tensile strength and the bending strength of the fiber-reinforced cement material do not depend upon the strength of the carbon fiber for the reinforcement but the adhesion or fixation between the cement matrix and the carbon fiber.
As attempts to improve the fixation of the carbon fiber in the cement matrix, there have been suggested a method in which the carbon fiber is oxidized with an oxidizing agent such as oxygen or ozone to make the surface of the fiber hydrophilic (KOJIMA et al., Tanso, No. 131, pp 161, 1987) and another method in which a fine cement and a fine aggregate are used to heighten dispersibility (SHIRAKAWA et al., the 4th, Concrete Engineering Annual Lecture Meeting, Lecture Booklet, pp 153, 1982). However, these methods are not satisfactory from the viewpoints of the performance and the manufacturing cost of the carbon fiber-reinforced cement material. Thus, a simple method for preparing the carbon fiber-reinforced cement material is desired in which characteristics inherent in the carbon fiber are utilized and the dependence upon the carbon fiber in the strength is heightened.
The present invention has been made under such a situation, and a major object of the present invention is to provide a method for preparing a carbon fiber-reinforced cement material having an enhanced fiber reinforcement effect by a simple process.